1. Field of the Invention
The present invention relates to an electromagnetic solenoid adapted to open and close a fluid control valve such as a flow-rate control valve, a pressure control valve, a changeover valve and the like.
2. Description of the Prior Art
FIG. 2 is a cross sectional view showing a conventional electromagnetic solenoid. In this FIG., reference numeral 1 designates a cylindrical casing having a fixed iron core 2 integrally formed with its end wall 1a, the casing 1 being closed at its open end opposite the end wall 1a by an end plate 3. The casing 1, the fixed iron core 2 and the end plate 3 jointly form a magnetic circuit. Housed in the casing 1 is a solenoid coil 4 which is wound around a bobbin or a winding frame 5 formed of synthetic resin. A movable iron core 6 is fixedly connected with an output rod 7 supported through a plain bearing 8 by the fixed iron core 2 for axial sliding movement relative thereto. Firmly fitted in the inner peripheral surface of the winding frame 5 is a sleeve 9 formed of a non-magnetic material for supporting the movable iron core 6 for axial sliding movement. The movable iron core 6 is biased toward the fixed iron core 2 under the action of a biasing spring 10. The electromagnetic solenoid constructed in the above manner is to be connected with a control valve 11 which is shown by the phantom line. In this case, though not shown in FIG. 2, the output rod 7 is biased in the leftward direction in FIG. 2 by a return spring (not shown) arranged in the control valve 11. The return spring in the control valve 11 is stronger than the spring 10 so that the movable iron core 6 is in the position shown in FIG. 2 when the solenoid coil 4 is not energized.
The above-mentioned conventional electromagnetic solenoid operates as follows. When the solenoid coil 4 is energized, the movable iron core 6 is caused to move by an electromagnetic force in the direction indicated by an arrow C in FIG. 2 toward the fixed iron core 2 against the biasing force of the return spring (not shown) arranged in the control valve 11.
With the above-described conventional electromagnetic solenoid, the casing and the fixed iron core 2 integrally formed therewith are difficult to fabricate and/or machine. Furthermore, the configuration and the length of extension of the fixed iron core 2 from the casing end wall 1a and hence the required operating characteristics of the solenoid can not be changed after fabrication thereof.